The present invention relates to image display apparatuses and image display methods and, more particularly, to an image display apparatus and method using a passive light modulation device and dynamically adjusting contrast and light source brightness according to an input video signal. Further, the image display apparatus and method of the present invention improve light-emitting efficiency of the light source at the time of dynamically adjusting intensity (light amounts) thereof according to the input signal.
As well known, a large number of image display apparatuses are used as screen display apparatuses for a television receiver, computer, and the like. Among those, a passive light modulation type apparatus typified by a liquid crystal display apparatus, displays images on a passive light modulation part, which does not emit light by itself (liquid crystal panel, for example). Therefore, the screen of such apparatus look dim compared with display apparatuses of a light-emitting type such as CRTs. To cope with this, passive light modulation type image display apparatuses are generally provided with a light source (backlight, for example) which emits light from the rear side of a passive light modulation part therein to increase visual brightness of display screen. Accordingly, brightness of the light source can be adjusted in addition to general contrast adjustment, thereby improving visibility of displayed images.
The levels of contrast and light source are basically adjusted manually by a user and fixedly set. In the recent years, however, to make the images more visible, various methods have been suggested to achieve dynamic adjustment of contrast and intensity of a light source (hereinafter, referred to as light adjustment) according to an input video signal that varies with time.
Such conventional methods for dynamically adjusting contrast and light source are exemplarily disclosed in Japanese Patent Laid-Open Publication Nos. 5-127608 and 8-201812 titled xe2x80x9cliquid crystal display apparatusxe2x80x9d. In the conventional adjustment methods disclosed in these publications, a maximum brightness level (MAX) and a minimum brightness level (MIN) of an input video signal are detected. When a difference between the maximum brightness level and the minimum brightness level is large, contrast is reduced, and is increased when the difference is small. Further, in the conventional adjustment methods, an average brightness level (APL) of the input video signal is detected. When the average brightness level is higher than a predetermined reference brightness level, brightness of the light source is reduced, and is increased when lower. As such, the conventional adjustment methods aim to always achieve constant display brightness.
In the conventional adjustment methods disclosed in the above publications, however, contrast adjustment (i.e., signal amplitude control) and light source brightness adjustment are separately performed (that means there is no correlation between both adjustments). Accordingly, the above described conventional adjustment methods cannot provide sufficient effect in improvement of a sense of contrast.
The light source is mainly implemented by a fluorescence lamp in view of light-emitting efficiency. General characteristics of the fluorescence lamp is now described by referring to FIG. 27 to FIG. 29. FIG. 27 is a diagram exemplarily showing a characteristic of a general fluorescence lamp, that is, a characteristic of lamp temperature to light emitting-efficiency. FIG. 28 is a diagram exemplarily showing a characteristic of lamp tube current to lamp temperature. Note that FIG. 28 shows a case where the fluorescence lamp is used as a back lamp, and shows a characteristic that the lamp temperature becomes 65xc2x0 C. at current i0. FIG. 29 is a diagram exemplarily showing a characteristic of lamp tube current to brightness.
First, as shown in FIG. 27, for the general fluorescence lamp in use, there exists a temperature at which its light-emitting efficiency reaches maximum due to vapor pressure of mercury inside the lamp tube (in the drawing, 65xc2x0 C.). Next, as shown in FIG. 28, the general fluorescence lamp, due to heat produced by itself, shows such a relation that the lamp temperature is in proportion to the lamp tube current. According to the characteristics shown in FIG. 27 and FIG. 28, the efficiency of brightness adjustment (light-emitting efficiency) of the fluorescence lamp is resultantly declined in either case of the lamp tube current being larger or smaller than the current i0, as shown in FIG. 29.
If taking this into consideration, the conventional adjustment methods as disclosed in the above publications are inevitably required to utilize a linear part of the characteristic shown in FIG. 29. This is because the methods aim to achieve constant visual brightness (display brightness) by adjusting the intensity of the light source based on the detected average brightness level. Accordingly, in the conventional adjustment methods, the light source cannot be efficiently used (that is, the maximum brightness cannot be obtained).
Further, the life of the lamp used as the light source varies with lamp tube current and temperature. Therefore, in the conventional image display apparatuses that adjust the intensity of the light source brightness according to a video signal, such a problem has been existed that, if the video signal is uneven in its characteristic, a lamp tube current (drive current) of a large value flows in the tube for a long time, thereby shortening the lamp life.
Therefore, a first object of the present invention is to provide an image display apparatus and an image display method capable of visually improving a sense of contrast without increasing power consumption of a light source by carrying out contrast adjustment (signal amplitude control) and brightness adjustment of the light source such that they correlate.
A second object of the present invention is to provide an image display apparatus and an image display method capable of dynamically and optimally adjusting the intensity of the light source according to an input video signal by utilizing a range in the vicinity of a characteristic to maximize the light-emitting efficiency of the light source.
Further, a third object of the present invention is to provide an image display apparatus and an image display method capable of dynamically and optically adjusting the intensity of the light source according to an input video signal while securing the life of the light source required as a product.
To achieve the objects above, the present invention has the following aspects.
A first aspect of the present invention is directed to an image display apparatus and method for displaying a video signal to be inputted on a passive light modulation part including a light source as an image. In the present image display apparatus and method, an amplitude of the video signal is dynamically adjusted to become a predetermined amplitude value. Then, brightness of the light source is adjusted according to amplitude adjustment so that the image displayed on the passive light modulation part based on the video signal after amplitude adjustment does not vary visually from a predetermined level. As such, according to the present image display apparatus and method, brightness adjustment of the light source is carried out to have correlation between amplitude adjustment, thereby not varying the visual average brightness level. Thereby, a sense of contrast can be visually improved without increasing average power consumption of the light source.
In the present invention, an average brightness level of each frame in the input video signal is preferably used as the predetermined level. In the following second and third aspects, disclosed are image display apparatuses and methods adjusting amplitude and brightness of the light source by using the average brightness level as the predetermined level.
The second aspect of the present invention is directed to an image display apparatus and method for displaying a video signal to be inputted on a passive light modulation part including a light source as an image. In the present image display apparatus and method, a maximum brightness level (MAX), a minimum brightness level (MIN), and an average brightness level (APL) of the video signal are each detected. Then, based on these levels, generated are signal control data indicating an instruction for amplification and light source control data for making the light source light at intensity that an average brightness level of the image displayed on the passive light modulation part based on the video signal after amplification becomes equivalent to the APL. Further, in accordance with the generated signal control data, the maximum amplitude of the video signal (a difference between MAX and MIN) is amplified to a width of a dynamic range for output to the passive light modulation part. In accordance with the generated light source control data, brightness control of the light source is carried out.
Here, the signal control data and the light source control data are preferably generated in the following manner. That is to say, newly received APL is compared with APL of the previous processing so that a level difference therebetween is determined. Then, control data in a range between that calculated in the previous processing and that calculated based on MAX and MIN of this time is adopted in a variable manner according to a variation of the level difference from the minimum value to the maximum value. Alternatively, it is determined whether a level difference between MAX and MIN is smaller than a predetermined value. If determined that the level difference is smaller than the predetermined value, control data in a range between that for a value without amplitude adjustment and light source brightness adjustment and that calculated based on MAX and MIN is adopted in a variable manner according to a variation of the level difference from the minimum value to the predetermined value. Accordingly, in the present image display apparatus and method, a sense of contrast is visually improved appropriately even for the video signal varied in type and mode, and in addition, although the effect of improvement in image quality is more or less reduced on each image basis, visual inappropriateness caused by excessive control is suppressed and sequence of images is displayed smoothly.
The third aspect of the present invention is directed to an image display apparatus and method for displaying a video signal to be inputted on a passive light modulation part including a light source as an image. In the present image display apparatus and method, MAX, MIN, and APL of the video signal are each detected. Then, based on these levels, calculated are a gain for amplifying the maximum amplitude of the video signal (a difference between MAX and MIN) to a width of an output dynamic range that is acceptable at the passive light modulation part and an offset indicating an amount for shifting a DC level so that the video signal after amplification falls within the output dynamic range. Further, the video signal is amplified with reference to APL and in accordance with the calculated gain. Still further, the DC level of the video signal after amplification is shifted in accordance with a value of the offset for output to the passive light modulation part. Then, light source brightness control is carried out in accordance with the offset for making the light source light at intensity that an average brightness level of the image displayed on the passive light modulation part based on the video signal after amplification becomes equivalent to APL.
Herein, when the video signal is previously subjected to gamma correction processing, the following process is carried out. That is to say, the video signal to be outputted to the passive light modulation part is subjected to reverse gamma correction processing that compensates the gamma correction processing applied thereto, and outputted to the passive light modulation part. On the other hand, the offset is subjected to the reverse gamma correction processing which is identical to that described above, and used for light source brightness control. Accordingly, in the present image display apparatus and method, a sense of contrast can be visually improved appropriately even with respect to the video signal previously subjected to the gamma correction processing.
As described, in the first to the third aspects, desclosed are the image display apparatuses and methods carrying out contrast adjustment and light source brightness adjustment for the system displaying a single screen. Next, in a fourth aspect, disclosed are an image display apparatus and method carrying out contrast adjustment and light source brightness adjustment for a system displaying two screens on one passive light modulation part.
The fourth aspect of the present invention is directed to an image display apparatus and method displaying two video signals to be inputted at a time on a passive light modulation part including a light source as images. In the present image display apparatus and method, MAX, MIN, and APL of any one of the video signals being a target for adjustment (main video signal) are each detected. Then, based on these levels, generated are signal control data indicating an instruction for amplification and light source control data for making the light source light at intensity that an average brightness level of the image displayed on the passive light modulation part based on the video signal after amplification becomes equivalent to APL. Further, the maximum amplitude of the main video signal (a difference between MAX and MIN) is amplified to a width of a dynamic range in accordance with the generated signal control data. The brightness of the light source is controlled in accordance with the generated light source control data. Still further, an amplitude of any one of the video signals other than the target for adjustment (sub-video signal) is amplified or attenuated according to the light source control data so that the effect of light source brightness adjustment applied to the main video signal is canceled for the sub-video signal. Then, the main video signal after amplification and the sub-video signal after amplification or attenuation is selectively switched in accordance with a timing of a switch signal supplied externally for output to the passive light modulation part. As such, in the present image display apparatus and method, contrast adjustment and light source brightness adjustment are carried out with respect to the main video signal, and correction canceling the effect of the light source brightness adjustment is carried out with respect to the sub-video signal. Thereby, a sense of contrast can be visually improved, appropriately and naturally for both screens in the system displaying two screens at the time.
As described, in the first to the fourth aspects, disclosed are the image display apparatuses and methods visually improving a sense of contrast without increasing power consumption of a light source by carrying out amplitude adjustment and brightness adjustment of the light source to have correlation. Next, in the following fifth to seventh aspects, disclosed are image display apparatuses and methods for dynamically and optimally adjusting the intensity of the light source according to an input video signal by utilizing a range in the vicinity of a characteristic at which the light-emitting efficiency of the light source reaches maximum.
The fifth aspect of the present invention is directed to an image display apparatus and method for displaying a video signal to be inputted on a passive light modulation part including a light source as an image. In the present image display apparatus and method, characteristic data corresponding to a characteristic amount of the video signal is calculated. Then, light adjustment control data for controlling the light source is calculated in accordance with a difference between predetermined reference data and the characteristic data. Further, based on reference light adjustment control data indicating a predetermined drive current at which the light-emitting efficiency of the light source reaches maximum, generated is another light adjustment control data used for controlling a value of the drive current of the light source to converge on the reference light adjustment control data only with respect to components that vary within a predetermined time period among the light adjustment control data. Then, in accordance with the another light adjustment control data, intensity adjustment of the light source is dynamically controlled by controlling the value of the drive current of the light source. As such, in the present image display apparatus and method, the temperature of the light source can be always controlled to be optimum, and therefore, the intensity of the light source can be dynamically adjusted under the condition that the light-emitting efficiency thereof always being maximum. Thereby, the efficiency of light adjustment can be improved than before.
The another light adjustment control data is generated in the following procedure, for example. First, only AC components that vary within a time period of a predetermined time constant are passed among the light adjustment control data. Herein, the time constant is preferably set not to exceed a time period in which the response characteristic of temperature variation of the light source is unsatisfied with respect to increment/decrement of the drive current of the light source. Then, the reference light adjustment control data and AC component light adjustment control data are added for generation. Accordingly, in the present image display apparatus and method, control can be carried out in such a manner that the light source temperature is always in the range in the vicinity of a characteristic to maximize the light-emitting efficiency (optimum temperature).
Further, preferably in the present image display apparatus and method, a physical amount of a vicinity of the light source may be detected, and according to the detection result, a value of the reference light adjustment control data may be dynamically varied so that to always maximize the light-emitting efficiency of the light source. Accordingly, in the present image display apparatus and method, brightness can be always adjusted dynamically under the condition to maximize the light-emitting efficiency of the light source, without being affected by the environmental temperature when in use.
A sixth aspect of the present invention is directed to an image display apparatus and method for displaying a video signal to be inputted on a passive light modulation part including a light source as an image. In the present image display apparatus and method, characteristic data corresponding to a characteristic amount of the video signal is calculated. Then, light adjustment control data for controlling the light source is calculated in accordance with a difference between predetermined reference data and the characteristic data. Further, based on reference light adjustment control data indicating a predetermined drive current to maximize the light-emitting efficiency of the light source and/or standard light adjustment control data, generated is another light adjustment control data used for controlling a value of the drive current of the light source to converge on the reference light adjustment control data and/or the standard light adjustment control data only with respect to components that vary within a predetermined time period among the light adjustment control data. Then, in accordance with the another light adjustment control data, intensity adjustment of the light source is dynamically controlled by controlling the value of the drive current of the light source. As such, in the present image display apparatus and method, the temperature of the light source can always be controlled to be optimum, and therefore, the intensity of the light source can be dynamically adjusted under the condition to always maximize the light-emitting efficiency thereof. Thereby, the efficiency of light adjustment can be improved.
Herein, the standard light adjustment control data is preferably the light adjustment control data indicating the drive current set in advance to secure standard brightness or the light adjustment control data indicating an average drive current set in advance to secure a lamp life.
Further, the another light adjustment control data is generated in the following procedure, for example. First, when the light adjustment control data is not less than the standard light adjustment control data, a data difference therebetween is calculated, and when the light adjustment control data is not more than the reference light adjustment control data, a data difference therebetween, and otherwise, a data difference of zero are calculated respectively. Next, only signal components that vary for a time period exceeding a predetermined time constant are extracted from the calculated variation difference data. Herein, the time constant is preferably set not to exceed a time period in which the response characteristic of temperature variation of the light source is unsatisfied with respect to increment/decrement of the drive current of the light source. Then, variation component light adjustment control data is subtracted from the light adjustment control for generation of another light adjustment control data. Accordingly, in the present image display apparatus and method, even for a case that the control reference value is required to be set as more than the drive current at which the light-emitting efficiency of the light source being maximum, intensity adjustment can be dynamically carried out for the brightness variation where the drive current is not less than the standard light adjustment control data while securing the standard brightness. For the brightness variation where the drive current is not more than the reference light adjustment control data, intensity adjustment can be dynamically carried out under the condition to maximize the light-emitting efficiency. Thereby, the efficiency of light adjustment can be improved.
Alternatively, when the light adjustment control data is not less than the standard light adjustment control data, a data difference therebetween is calculated, and otherwise, a data difference of zero is calculated. Next, only signal components that vary for a time period exceeding a predetermined time constant are extracted from the calculated variation difference data. Herein, the time constant is preferably set not to exceed a time period in which the response characteristic of temperature variation of the light source is unsatisfied with respect to increment/decrement of the ad drive current of the light source. Then, variation component light adjustment control data is subtracted from the light adjustment control for generation of another light adjustment control data. As Accordingly, in the present image display apparatus and method, even for a case that the control reference value is required to be set as more than the drive current at which to maximize the light-emitting efficiency of the light source, intensity adjustment can be dynamically carried out for the brightness variation where the drive current not less than the standard light adjustment control data while securing the standard brightness. Thereby, the efficiency of light adjustment can be improved.
A seventh aspect of the present invention is directed to an image display apparatus and method for displaying a video signal to be inputted on a passive light modulation part including a light source as an image. In the present image display apparatus and method, MAX, MIN, and APL of the video signal are each detected. Then, based on these levels generated are signal control data indicating an instruction for amplification and light source control data for making the light source light at intensity that an average brightness level of the image displayed on the passive light modulation part based on the video signal after amplification becomes equivalent to APL. Further, in accordance with the signal control data, the maximum amplitude of the video signal (a difference between MAX and MIN) is amplified to a width of a dynamic range. Further, based oil reference light adjustment control data indicating a predetermined drive current to maximize the light-emitting efficiency of the light source, generated is another light source control data used for controlling a value of the drive current of the light source to converge on the reference light adjustment control data only with respect to components that vary within a predetermined time period among the light adjustment control data. Then, light source brightness is dynamically controlled by controlling the value of the drive current of the light source in accordance with the another light source control data. As such, in the present image display apparatus and method, a sense of contrast can be visually improved without increment in average power consumption of the light source by carrying out brightness adjustment of the light source to have correlation with amplitude adjustment, thereby not varying a visual average brightness level. Further, in the present image display apparatus and method, the temperature of the light source can be controlled always to be the optimum temperature. Accordingly, the intensity of the light source can be always adjusted under the condition to always maximize the light-emitting efficiency, capable of improving the efficiency of light adjustment more.